Method and apparatus for delivery of metadata synchronized to multimedia contents

ABSTRACT

A metadata transmitter synchronized with multimedia contents comprises: a multimedia contents authoring unit for generating and editing multimedia contents; a multimedia contents format converter for compressing the multimedia contents, converting them into a transmission format, and outputting them; a metadata authoring unit for generating and editing metadata for describing the multimedia contents, the metadata including transmission types and transmission information; a metadata format converter for converting the metadata into binary codes, converting the converted metadata into a synchronization format for synchronization with the multimedia contents and a transmission format, and outputting them; and a multiplexer for multiplexing the multimedia contents format and the metadata format respectively output from the multimedia contents format converter and the metadata format converter into a stream, and outputting it.

The present patent application is a non-provisional application ofInternational Application No. PCT/KR02/00137, filed Jan. 30, 2002.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Korea Patent Application No. 2001-4341filed on Jan. 30, 2001 in the Korean Intellectual Property Office, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an apparatus and method forsynchronizing metadata with multimedia contents, and transmitting them.

(b) Description of the Related Art

Metadata description methods for representing Essence, which ismultimedia contents, and their standardization activities are now inprogress. However, prior art only disclose metadata description methodsand do not include synchronization and transmission methods of themultimedia contents and related metadata. The specifications of themetadata description method are found from MPEG, SMPTE, and TV.Anytime.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method forsynchronizing metadata with multimedia contents, and transmitting them,and for a terminal to receive the multimedia contents including themetadata and use them.

In one aspect of the present invention, a metadata transmittersynchronized with multimedia contents comprises: a multimedia contentsauthoring unit for generating and editing multimedia contents; amultimedia contents format converter for compressing the multimediacontents, converting them into a transmission format for synchronizationand transmission, and outputting them; a metadata authoring unit forgenerating and editing metadata for describing the multimedia contents,the metadata including transmission types and transmission information;a metadata format converter for converting the metadata into binarycodes, converting the converted metadata into a synchronization formatfor synchronization with the multimedia contents and a transmissionformat for transmission, and outputting them; and a multiplexer formultiplexing the multimedia contents format and the metadata formatrespectively output from the multimedia contents format converter andthe metadata format converter into a stream, and outputting it.

The metadata format converter comprises: a metadata synchronizationformat converter for converting the metadata transmitted from themetadata authoring unit into binary codes, and converting them into asynchronization format for synchronization with the multimedia contents;and a metadata transmission format converter for converting the dataoutput from the metadata synchronization format converter, according toa transmission format.

In another aspect of the present invention, a method for synchronizingmetadata with multimedia contents and transmitting them comprises: (a)generating and editing metadata for describing multimedia contents, themetadata including transmission types and transmission information; (b)converting the metadata into binary codes, and converting the convertedmetadata into a synchronization format for synchronization with themultimedia data; and (c) converting the metadata converted in (b) into atransmission format for transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention:

FIG. 1 shows a metadata transmission system according to a preferredembodiment of the present invention;

FIG. 2 shows a metadata format converter according to a preferredembodiment of the present invention;

FIG. 3 shows a flowchart of a method for transmitting metadatasynchronized with MPEG-2 data according to a preferred embodiment of thepresent invention;

FIG. 4 shows definitions of stream identifiers used for transmitting themetadata synchronized with MPEG-2 data according to a preferredembodiment of the present invention;

FIG. 5 shows definitions of stream-type values used for transmitting themetadata synchronized with MPEG-2 data according to a preferredembodiment of the present invention;

FIG. 6 shows an exemplified PES packet for synchronizing synchronousmetadata with MPEG-2 data according to a preferred embodiment of thepresent invention; and

FIG. 7 shows an exemplified PES packet for synchronizing synchronizedmetadata with MPEG-2 data according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inventor(s) ofcarrying out the invention. As will be realized the invention is capableof modification in various obvious respects, all without departing fromthe invention. Accordingly, the drawings and description are to beregarded as illustrative in nature, and not restrictive.

FIG. 1 shows a metadata transmission system according to a preferredembodiment of the present invention. As shown, the metadata transmissionsystem comprises a multimedia contents authoring unit 100; a multimediacontents format converter 200; a metadata authoring unit 300; a metadataformat converter 400; and a multiplexer 500.

The multimedia contents authoring unit 100 generates multimediacontents, edits them, and outputs them to the multimedia contents formatconverter 200. In this instance, the multimedia authoring processincludes processes of generating and editing the multimedia data, andthe editing process does not specify a particular process exceptingauxiliary tasks including correcting and adding generated multimediadata.

The multimedia contents format converter 200 compresses the multimediacontents input from the multimedia contents authoring unit 100, convertsthem into transmission format data for synchronization and transmission,and outputs them to the multiplexer 500. The multimedia contents formatconverter 200 performs synchronization format conversion andtransmission format conversion. According to the embodiment of thepresent invention, the synchronization format includes: MPEG-2 PES(packetized elementary stream) packets, MPEG-4 SL (sync layer) packets,MPEG-4 FlexMux packets, and RTP (real time protocol) standardspecifications, and the transmission format includes: MPEG-2 TS(transport stream), IP (Internet protocol), and ATM (asynchronoustransfer mode) standard specifications.

That is, the multimedia contents format converter 200 compresses themultimedia contents using at least one method of standard specificationsof MPEG-1, MPEG-2, MPEG-4, H.261, H.263, and H.26L. In other words, forexample, it compresses some of the multimedia data using the MPEG-4standard and compresses a remaining portion of the multimedia data usingthe H.263 standard, so the whole of the multimedia data may comprise theMPEG-4 data and the H.263 data.

After the compression process, the multimedia contents format converter200 converts the compressed multimedia contents into a synchronizationformat using at least one standard specification of the MPEG-2 PESpacket, the MPEG-4 SL packet, the MPEG-4 FlexMux packet, and the RTPpacket, and converts them into a transmission format using at least onestandard specification of the MPEG-2 TS, the IP, and the ATM.

The metadata authoring unit 300 generates and edits metadata fordescribing the multimedia contents, and outputs them to the metadataformat converter 400. According to the embodiment of the presentinvention, the metadata authoring unit 300 performs an authoring processusing one of MPEG-7, SMPTE (Society of Motion Picture and TelevisionEngineers), TV Anytime, and EBU (European broadcasting union) standardspecifications on the XML (extensible markup language). In thisinstance, the metadata authoring unit 300 concurrently generatestransmission types and transmission information at the time ofauthoring.

The metadata format converter 400 converts the metadata input from themultimedia contents authoring unit 100 into binary codes, converts theminto a transmission format for synchronization and transmission, andoutputs them to the multiplexer 500. The metadata format converter 400performs synchronization format conversion and transmission formatconversion. The synchronization format includes data characteristics,relations with whole streams, time information, and length informationof a charged load, and the transmission format representing a formatneeded for transmitting packetized data includes sequence informationand data types of the charged load.

That is, the metadata format converter 400 converts the metadata intobinary codes using at least one of the MPEG-7, the SMPTE, theTV-Anytime, and the EBU standard specifications, converts the convertedmetadata into a synchronization format using at least one of the MPEG-2PES packet, the MPEG-4 SL packet, the MPEG-4 FlexMux packet, and the RTPpacket standard specifications, and converts them into a transmissionformat using at least one of the MPEG-2 TS, the IP, and the ATM standardspecifications.

The multiplexer 500 multiplexes the multimedia contents input from themultimedia contents format converter 200 and the metadata input from themetadata format converter 400 into a single stream, and transmits it toa transmission network 600.

An interactive terminal 700 processes the stream transmitted via thetransmission network 600 so that a user may use desired multimediacontents and metadata.

FIG. 2 shows the metadata format converter 400 according to a preferredembodiment of the present invention. As shown, the metadata formatconverter 400 comprises: a metadata synchronization format converter420; and a metadata transmission format converter 440.

The metadata synchronization format converter 420 converts theXML-language metadata transmitted from the metadata authoring unit 300into binary codes, and converts them into a synchronization format. Themetadata transmission format converter 440 converts the data transmittedfrom the metadata synchronization format converter 420 intopredetermined data according to respective transmission formats, andoutputs them to the multiplexer 500.

In this instance, the subsequent two methods can be used to synchronizethe metadata according to the preferred embodiment of the presentinvention.

The first method is to packetize the metadata into packets identicalwith those for transmitting speech and image data. In detail, themetadata are packetized in the sequential order of the RTP packet andthe IP packet in the Internet network case, they are packetized into TSpackets after PES or section packetizing in the broadcasting networkcase, and they are sequentially packetized in the order of the SL packetand the FlexMux packet in the MPEG-4 case. In this instance, since theRTP packet, the PES packet, or the SL packet for packetizing themetadata has decoding time or output time value, it is required topacketize the metadata according to the time value. However, the firstmethod is required to support each network's decoder model according tocategories of transmitting networks. That is, since it is needed for thedecoder to analyze the packets that have respective networks' timevalues and to connect to a decoder for decoding the metadata, it isimpossible to amend to each system decoder model.

The second method is to convert the metadata into a synchronizationformat and synchronize it with multimedia data. This method enables tosynchronize data and transmit them with no relation to the transmissionnetworks. In this instance, it is necessary for the decoder model to usethe decoder model of the metadata without using that of eachtransmission network. Also, since the metadata synchronization formathas independent decoding time and output time values, it enables tooperate the decoder model and support synchronization. In this instance,the decoding time value and the output time value refer to themetadata's time default value and time reference value to represent themetadata's decoding time and output time.

The metadata synchronization format converter 420 comprises: a metadatabinary code converter 421; a metadata synchronous format converter 422;a packetizing controller 423; an RTP packetizer 424; an MPEG-2packetizing controller 425; a PSI (program specific information)generator 426; a PES packetizer 427; a section packetizer 428; and an SLpacketizer 429.

The metadata binary code converter 421 converts the metadata stored inthe XML language into binary codes so as to transmit the metadatagenerated from the metadata authoring unit 300. The metadata synchronousformat converter 422 converts the binary codes into a metadatasynchronization format so as to synchronize and transmit them with norelation to the transmission networks. In this instance, the metadatasynchronization format independently has decoding time and output timevalues so as to operate the decoder model and support synchronization.Also, the decoding time value and the output time value refer to themetadata's time default value and time reference value to represent themetadata's decoding time and output time.

The packetizing controller 423 selects a metadata's transmission networkso as to make the transmission network of the multimedia contentscoincide with that of the metadata.

The RTP packetizer 424 packetizes the metadata into an RTP, and the SLpacketizer 429 packetizes synchronous, synchronized, and asynchronousmetadata into an MPEG-4 SL packet.

In this instance, the technical terms “synchronous” and “synchronize”are generally used in data broadcasting. To synchronize is to match animage frame with an audio frame at a time axis so as to regulate syncsof images and speech, or to match an axis of additional data with a timeaxis that matches the speech with the images. To be synchronous is tomatch additional data with another independently-operating time axisthat does not correspond to the time axis for synchronizing the speechor images.

The MPEG-2 packetizing controller 425 classifies the metadata input tobe packetized into an MPEG-2 system specification, as the metadata thathave synchronization time values and other metadata that do not havethem, outputs the metadata that have synchronization time values to thePES packetizer 427, outputs the metadata that do not havesynchronization time values to the section packetizer 428, and transmitsPSI information including metadata transmission types and transmissioninformation to the PSI generator 426.

In this instance, the PSI for representing information defined for adecoder to decode programs includes: a PAT (program association table);a PMT (program map table); an NIT (network information table); and a CAT(conditional access table). The PAT and the PMT represent information onprogram elements that form a program, the NIT shows information on thetransmission networks, the CAT indicates information on conditionalreceiving, and the. PES represents a data structure used for carryingelementary streams.

Since the metadata are transmitted in the PES or sections, the PSIgenerator 426 receives a transmission type and transmission informationand records them on the PMT section so as to provide related terminalinformation.

The PES packetizer 427 packetizes the synchronous and synchronizedmetadata into an MPEG-2 PES. Since a PES packet header includes a DTS(decoding time stamp) and a PTS (presentation time stamp),synchronization is possible based on them.

The section packetizer 428 packetizes asynchronous metadata intosections. Since a section header does not include synchronous andsynchronized time values, it is used for transmitting asynchronousmetadata.

The metadata transmission format converter 440 comprises: an IPpacketizer 441; a TS packetizer 442; and a FlexMux packetizer 443. TheIP packetizer 441 packetizes the metadata into an IP, and the FlexMuxpacketizer 443 packetizes the metadata into a FlexMux.

In this instance, the FlexMux represents a multiplexing method ofoptions provided by the MPEG-4 system. That is, the FlexMux packet isused for reducing an overhead of a transmission multiplexer (TranMux) orallocating a channel of the transmission multiplexer when multiplexing aplurality of streams. In general, the MPEG-4 stream is to be packetizedinto an SL packet in a sync layer, but the overhead can be reduced bypacketizing one or a plurality of SL packets into a single FlexMuxpacket. Also, each MPEG-4 stream together with a logical channel is tobe transmitted to a terminal from a server, and the FlexMux packetallocates logical channels for the respective MPEG-4 streams.

The TS packetizer 442 packetizes a PMT table input from the PSIgenerator 426, metadata input from the PES packetizer 427, and metadatainput from the section packetizer 428 into transport streams (TS).

A method for using MPEG-2 data as multimedia contents, synchronizing themetadata with the multimedia contents, and transmitting them in adigital broadcasting will now be described.

FIG. 3 shows a flowchart of a method for synchronizing the metadata withthe MPEG-2 data and transmitting them according to a preferredembodiment of the present invention.

When metadata are input from the metadata authoring unit 300 and themetadata binary code converter 421 in step S9, the input metadata areanalyzed in step S10. In this instance, it is determined whether theyneed to be synchronized with the MPEG-2 data in step S11, and whenneeded, they are packetized into PES packets in step S12, and when notneeded, they are packetized into private sections in step S13. Also, themetadata are analyzed to generate PSI in step S14, and the generatedPSI, the PES, or the data packetized into private sections arepacketized into TS packets in step S15. The TS-packetized metadata aremultiplexed with MPEG-2 audio/video TS through an input of asynchronization initial value to be output as a single TS in step S16.In a detailed method for synchronizing the metadata with the MPEG-2data, a metadata time default value and a metadata time reference valueare defined and used so as to synchronize the metadata with a systemtime reference value, that is, an STC (system time clock), and a programtime reference value, that is, a PCR (program clock reference) definedby the MPEG-2 system standard.

Since the STC defined by the MPEG-2 system standard is an STC operatingat 27 MHz, the STC is to be cooperated with the metadata time defaultvalue as a basic condition for synchronizing the metadata with theMPEG-2 data, which is expressed in Equation 1.f _(STC)(t)/f _(MetadataTimeBase)(t)=+Integer  Equation 1

-   -   where f_(STC)(t) represents a system clock signal of 27 MHz, and        f_(MetadataTimeBase)(t) indicates a metadata time default value.

Further, since the PCR defined by the MPEG-2 system standard is a PCRsampled by 90 KHz, the metadata time reference value is divided by theinteger of 90 KHz so as to synchronize the metadata with the PCR, whichis expressed in Equation 2.(f _(STC)(t)/300)f _(MetadataClockReference)=+Integer  Equation 2

-   -   where (f_(STC)(t)/300) represents 90 KHz, and        f_(MetadataClockReference) indicates a metadata time reference        value.

For further detailed description of Equations 1 and 2, in the MPEG-2system, the system clock signals are to be timed at 27 MHz so as tomatch the operation of the encoder and the decoder. For this purpose,the operation of the encoder at 27 MHz is to be provided to the decoder,which is enabled by transmitting the PCR that are values sampled at 90KHz. The reason for transmitting the values sampled at 27 MHz/300=90 KHzis to maintain the compatibility between the MPEG-1 and the MPEG-2,since the MPEG-1 operates at 90 KHz. In this instance, Equation 1represents that since the system clock of multimedia data operates at 27MHz, the clock of the metadata is to operate at a clock signal dividedby an integer corresponding to this, thereby enabling synchronizationbetween them. In the like manner, Equation 2 shows that a metadata timereference value is to have a time reference value, with respect to themultimedia data transmitting a time reference value sampled by 90 KHz,as many as the number obtained by dividing 90 KHz by an integer so asthus to enable synchronization between them.

In the preferred embodiment of the present invention, in order tosynchronize the metadata that require synchronization with the MPEG-2data and transmit them, the metadata are packetized into access unitsusing the MPEG-2 system standard. That is, to synchronize the metadatawith the MPEG-2 data, the metadata are packetized into packets using thePES packets as defined by the MPEG-2 system standard, and they aretransmitted using the TS. In order to packetize the metadata into PFSpackets through a detailed implementation method for synchronizing themetadata with the MPEG-2 data, a stream identifier (stream_id) of a PESpacket header defined by the MPEG-2 system standard is extended asfollows.

The stream identifier (stream_id) of the PES packet for transmitting themetadata is a field that represents what category of data the chargedload of the PES packet is. Stream identifier values for the metadata arenot defined in the current international standard, but the presentembodiment defines a stream_id for the metadata and uses it, andaccordingly, the metadata may be carried on the charged load of the PESpacket to be transmitted, which can be expressed as follows.

PES_packet( ) {   Packet_start_code_prefix   Stream_id = Metadata stream  PES_packet_length   . . . . . . }

In this instance, a value 0×FC is allocated as a stream identifier for anewly defined metadata stream as shown in FIG. 4.

Also, in the preferred embodiment of the present invention, in order totransmit the metadata that do not require synchronization, the metadataare packetized using the MPEG-2 system standard. In order to transmitthe metadata without synchronizing them, the metadata are packetizedusing the private sections, and they are transmitted using the TS asdefined by the MPEG-2 system standard.

In the preferred embodiment of the present invention, in order totransmit the metadata and apply them to a terminal, a message that themetadata are transmitted is reported to the terminal by using the MPEG-2system standard. That is, in order to report a metadata transmissionnotice to the terminal using the MPEG-2 system, a stream type of a PMTtable header defined by the MPEG-2 system standard is extended asfollows.

TS_program_map_section ( ) {   table_id   section_syntax_indicator   ‘0’  . . .     // Video     stream_type = 0×03 (ISO/IEC 13818-2 Video)    reserved     elementary_PID     // Audic     stream_type = 0×04(ISO/IEC 13818-3 Audio)     reserved     elementary_PID     . . .     .. .     // Metadata     stream_type = 0×15 (Metadata stream carried inPES packets)     reserved     elementary_PID     stream_type = 0×16(Metadata stream carried in Private Section)     reserved    elementary_PID     . . .   }   CRC_32 }

As described above, the PMT represents information on the element bitstreams configuring a program, defines identifiers of respective elementbit streams, and adds descriptors to show information on detailedelement bit streams. However, since the current standard does not havestream_type values for the metadata in the PMT table in a similar manneras definition of stream_id, a stream_type value is to be set so as toconfigure the metadata into data related to a single program. Hence, thepresent invention defines and uses the stream_type value to synchronizethe multimedia data with the metadata and transmit them.

As shown in FIG. 5, the stream-type values for the newly definedmetadata stream have a value of 0×15 in the case of the metadatatransmitted to the PES packet, and a value of 0×16 in the case of themetadata transmitted to the private section.

Finally, in the preferred embodiment of the present invention, in orderto synchronize the metadata that require synchronization with the MPEG-2data and transmit them, a CTS (composition time stamp)/DTS (decodingtime stamp) time value of a metadata access unit is used as an input ofa PTS (presentation time stamp)/DTS time value when packetizing themetadata into PES packets.

The metadata for being synchronized with the MPEG-2 data are classifiedin two ways. The first is as synchronous metadata, and the second is assynchronized metadata. Since the synchronous metadata stream isorganically operated, the synchronous metadata can be synchronized withthe multimedia contents by adding a synchronization initial value(Offset) to each CTS time value of the metadata stream to generate a PTSvalue, which is expressed in Equation 3.PTS(t)=CTS(t)+“Offset”  Equation 3

FIG. 6 shows a PES packet format for synchronizing the metadata with theMPEG-2 data.

Since the synchronized metadata is not organically operated, thesynchronized metadata can be synchronized with the MPEG-2 data byinputting each CTS time value of the metadata stream through a valueidentical with that of a PTS time value, which can be expressed as inEquation 4.PTS(t)=CTS(t)   Equation 4

FIG. 7 shows a PES packet format for synchronizing the synchronizedmetadata with the MPEG-2 data. Through the above process, thesynchronous and synchronized metadata can be synchronized with themultimedia contents, and they are packetized into 188-byte TS packetsand multiplexed with input MPEG-2 audio/video TS so as to transmit them.

According to the present invention, a detailed implementation method forsynchronizing the metadata used as additional information in the digitalbroadcasting with the MPEG-2 data and transmitting them is provided,thereby enabling transmitting the metadata in real-time, enabling theuser's random access, and applying the two kinds of data in variousways.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

1. A metadata transmitter for synchronizing metadata with multimediacontent and transmitting the synchronized metadata and multimediacontent comprising: a multimedia content authoring unit for generatingmultimedia content; a multimedia content format converter forcompressing the generated multimedia content, and converting thecompressed content into a format suitable for synchronization andtransmission; a metadata authoring unit for generating metadatadescribing the multimedia content, the metadata including transmissiontypes and transmission information; a metadata format converter forconverting the metadata into binary codes, converting the binary codesinto a format suitable for synchronization with the multimedia contentsand a format suitable for transmission; and a multiplexer formultiplexing the converted multimedia contents and the converted binarycodes respectively output from the multimedia contents format converterand the metadata format converter into a stream, and outputting thestream.
 2. The transmitter of claim 1, wherein the metadata formatconverter comprises: a metadata synchronization format converter forconverting the metadata from the metadata authoring unit into saidbinary codes, and converting said binary codes into said format suitablefor synchronization with the multimedia content; and a metadatatransmission format converter for converting the data output from themetadata synchronization format converter, to said format suitable fortransmission.
 3. The transmitter of claim 2, wherein thesynchronization-format includes a decoding time value and an output timevalue.
 4. The transmitter of claim 3, wherein the decoding time valueand the output time value include a time default value and a timereference value of the metadata.
 5. The transmitter of claim 2, whereinthe metadata synchronization format converter comprises: a metadatabinary code converter for converting the metadata from the metadataauthoring unit into binary codes; a metadata synchronous formatconverter for converting the converted binary codes into a metadatasynchronous format including a metadata time default value and ametadata time reference value; an MPEG-2 packetizing controller forclassifying the metadata output by the metadata synchronous formatconverter as metadata that have a synchronized time value and metadatathat do not have a synchronized time value, packetizing the metadatathat have a synchronized time value into packetized elementary stream(PES) packets, packetizing the metadata that do not have a synchronizedtime value into sections, and generating program specific information(PSI) including metadata transmission types and transmissioninformation; a PSI generator for writing the PSI output by the MPEG-2packetizing controller in a program map table (PMT) section; a PESpacketizer for packetizing the metadata that require synchronization andare output from the MPEG-2 packetizing controller into PES packets; anda section packetizer for packetizing the metadata that do not requiresynchronization and are output from the MPEG-2 packetizing controllerinto sections.
 6. The transmitter of claim 5, wherein the metadatasynchronization format converter further comprises: a real time protocol(RTP) packetizer for packetizing the metadata output from the metadatasynchronous format converter into an RTP; a sync layer (SL) packetizerfor packetizing synchronous metadata, synchronized metadata, andasynchronous metadata output from the metadata synchronous formatconverter into MPEG-4 SLs; and a packetizing controller for selectingone of the RTP packetizer, the MPEG-2 packetizing controller, and the SLpacketizer, and transmitting the metadata output from the metadatasynchronous format converter so as to match a transmission network ofthe multimedia contents with that of the metadata.
 7. The transmitter ofclaim 5, wherein the time default value used for the metadatasynchronous format is obtained by dividing a time reference value thatis system time clock (STC) defined by the MPEG-2 system standard by aninteger, and the metadata time reference value used for the metadatasynchronous format is obtained by dividing a program time referencevalue that is a program clock reference (PCR) by an integer.
 8. Thetransmitter of claim 5, wherein the PES packetizer extends a streamidentifier of a PES packet header defined by the MPEG-2 system standardto packetize the metadata that require synchronization into PES packets.9. The transmitter of claim 8, wherein the metadata that requiresynchronization are synchronous metadata, and a presentation time stamp(PTS) used for a format of the PES packet is a value obtained by addingan offset value to a composition time stamp (CTS) of a metadata accessunit.
 10. The transmitter of claim 8, wherein the metadata that requiresynchronization are synchronization metadata, and a presentation timestamp (PTS) used for a format of the PES packet is matched with acomposition time stamp (CTS) of a metadata access unit.
 11. Thetransmitter of claim 5, wherein the PSI generator extends a stream typeof a PMT table header defined by the MPEG-2 system standard so as tonotify a terminal of a metadata transmission notice.
 12. A method forsynchronizing metadata with multimedia content and transmitting themetadata and multimedia content comprising: (a) generating metadatadescribing multimedia content, the metadata including transmission typesand transmission information; (b) converting the metadata into binarycodes, and converting the binary codes into a format suitable forsynchronization with the multimedia data, wherein the synchronizationformat includes a decoding time value and an output time value, whereinthe synchronization format includes a decoding time value and an outputtime value; and (c) converting the converted metadata into a formatsuitable for transmission.
 13. The method of claim 12, furthercomprising: (d) multiplexing said multimedia content and the metadatasuitable for transmission into a stream.
 14. The method of claim 12,wherein the decoding time value and the output time value include a timedefault value and a time reference value of the metadata.
 15. The methodof claim 12, wherein said converting the metadata into binary codescomprises: converting the generated metadata into binary codes;converting the binary codes into a metadata synchronous format includinga metadata time default value and a metadata time reference value;classifying the metadata output from the metadata synchronous formatconverter into metadata that have a synchronized time value and metadatathat do not have a synchronized time value, and program specificinformation (PSI) including metadata transmission types and transmissioninformation; writing the PSI in a program map table (PMT) section;packetizing the metadata into packetized elementary stream (PES) packetswhen the metadata require synchronization; and packetizing the metadatainto sections when the metadata do not require synchronization.
 16. Ametadata transmitter for synchronizing metadata with multimedia contentscomprising: a metadata authoring unit for generating metadata describingthe multimedia content, the metadata including transmission types andtransmission information; a metadata synchronization format converterfor converting the metadata into binary codes, and converting the binarycodes into a format suitable for synchronization with the multimediacontent; a metadata transmission format converter for converting dataoutput from the metadata synchronization format converter to a formatsuitable for transmission; and a multiplexer for multiplexing themultimedia content and the metadata output from the metadatatransmission format converter into a stream, and outputting the stream.17. The transmitter of claim 16, wherein the synchronization formatincludes a decoding time value and an output time value, and thedecoding time value and the output time value include a time defaultvalue and a time reference value of the metadata.
 18. The transmitter ofclaim 16, wherein the metadata synchronization format convertercomprises: a metadata binary code converter for converting the metadatagenerated by the metadata authoring unit into binary codes; a metadatasynchronous format converter for converting the converted binary codesinto a metadata synchronous format including a metadata time defaultvalue and a metadata time reference value; an MPEG-2 packetizingcontroller for classifying the metadata output by the metadatasynchronous format converter as metadata that have a synchronized timevalue and metadata that do not have a synchronized time value,packetizing the metadata that have a synchronized time value intopacketized elementary stream (PES) packets, packetizing the metadatathat do not have a synchronized time value into sections, and generatingprogram specific information (PSI) including metadata transmission typesand transmission information; a PSI generator for writing the PSI outputby the MPEG-2 packetizing controller in a program map table (PMT)section; a PES packetizer for packetizing the metadata that requiresynchronization and are output from the MPEG-2 packetizing controllerinto PES packets; and a section packetizer for packetizing the metadatathat do not require synchronization and are output from the MPEG-2packetizing controller into sections.